This invention relates generally to fluid processing, and specifically to process flow measurement and control. In particular, the invention concerns magnetic flowmeters.
Magnetic flowmeters (or mag meters) measure flow by Faraday induction, an electromagnetic effect. The meter energizes a coil (or coils) to generate a magnetic field across a pipe section, and the magnetic field induces an electromotive force (EMF) across the process flow. The flow velocity is proportional to the induced EMF, and the volumetric flow rate is proportional to the flow velocity and flow area.
In general, electromagnetic flow measurement techniques are applicable to water-based fluids, ionic solutions and other conducting liquid flows. Specific uses include water treatment facilities, high-purity pharmaceutical manufacturing, hygienic food and beverage production, and chemical processing, including hazardous and corrosive process flows. Magnetic flowmeters are also employed in the hydrocarbon fuel industry, including hydraulic fracturing techniques utilizing abrasive and corrosive slurries, and in other hydrocarbon extraction and processing methods.
Magnetic flowmeters provide fast, accurate flow measurements in applications where differential pressure-based techniques are disfavored because of the associated pressure drop (for example, across an orifice plate or Venturi tube). Magnetic flowmeters can also be used when it is difficult or impractical to introduce into the process flow a mechanical element, such as turbine rotor, vortex-shedding element or Pitot tube.
A magnetic flowmeter determines a flow rate of a conductive fluid flowing through a conduit or pipe by measuring a voltage generated across the fluid in a direction perpendicular to the fluid flow as the fluid moves through a magnetic field generated by the flowmeter. The voltage is measured between two electrodes that are in contact with the fluid and are positioned on opposite sides of the pipe. The pipe walls must be either electrically non-conductive or, if conductive, have an electrically non-conductive liner to keep from shorting out the voltage generated across the fluid flow. If the pipe wall is conductive, the two electrodes must also be electrically insulated from the pipe wall and must penetrate the non-conductive liner to accurately measure the generated voltage.
Magnetic coils having a saddle shape, referred to simply as saddle coils, typically are utilized in magnetic flowmeters to generate the magnetic field. In a typical magnetic flowmeter, saddle coils are secured to opposite exterior portions of a cylindrical pipe, through which a fluid passes.
A typical saddle coil for a magnetic flowmeter is made by wrapping a coil winding about a permanent fixture in a flat (i.e., planar) orientation, then wrapping the winding with a tape or fiberglass material that covers top and bottom portions of the winding. Next, the winding is removed from the fixture and placed over part of a cylinder to bend it to a desired saddle shape. Then a coating on the winding is bonded together to harden the winding in the desired shape. Lastly, the winding assembly is secured to a mounting location on a pipe using conventional threaded mechanical fasteners (e.g., studs, bolts and clamps). Tape (or fiberglass) is utilized because an insulative coating on the wire of the winding is relatively thin, and during use the saddle coil may be exposed to vibrations and other conditions that can wear away the insulative coating and pose a risk of shorting the wire to the pipe on which it is installed. The tape also helps hold the wire of the winding together during bending and bonding operations. However, the tape and clamps utilized with prior art saddle coils are cumbersome during fabrication.
Assembly of magnetic flowmeters is labor intensive, complicated, and prone to variability and errors. Currently, very few of the parts used in the magnetic flowmeter are integrated or multifunction, which increases parts count, complicates assembly, and increases cost.